1. Field of the Invention
The present application generally relates to rotors for aircraft and specifically relates to a multiple-yoke main rotor assembly for aircraft.
2. Description of Related Art
Demand is increasing for rotary-wing aircraft, such as helicopters and tiltrotors, to provide more thrust, higher speeds, and carry heavier loads and/or heavier fuselages. For example, there is a demand for more powerful tiltrotor aircraft. Where performance criteria such as these are to be increased, the functional systems of the rotary-wing aircraft must be improved to provide the desired resultant performance enhancements. The rotor system is one of the many functional systems which require improvement in order to meet the demand for improved rotary-wing aircraft performance.
Rotary-wing aircraft have at least one rotor for providing lift and propulsion forces. These rotors have at least two airfoil blades connected to a central hub, and the hub is mounted on a rotatable mast driven in rotation by an engine or motor. These blades may be adjustable for pitch angle, and the pitch angle is typically controlled by a swashplate assembly and linkage for connecting a rotating portion of the swashplate assembly to each blade.
Existing rotor assemblies have many configurations. One example of a prior-art system is a teetering rotor, in which a yoke attaches the blades to a central hub, and the yoke is pivotally attached to the mast, allowing for the yoke to teeter about a central flap axis that intersects the mast axis. FIG. 1 is a schematic view of a teetering system 11 mounted to a mast 13. Yoke 15 has two blades 17 attached at opposite ends of yoke 15, and yoke 15 is pivotally attached to mast 13 for rotation therewith about mast axis 19. To provide for a pivoting connection to mast 13, opposing cylindrical trunnions 21 extend radially from mast 13, defining flap axis 23. This configuration allows the rotor assembly of yoke 15 and blades 17 to freely pivot, or “teeter,” about flap axis 23 relative to mast 13, as indicated by directional arrows 25. This type of rotor system has been used, for example, as a main rotor system on the Bell UH-1 Iroquois helicopter.
A twin teetering system 27, as shown in schematic form in FIG. 2, has been used as a tail-rotor system, such as in the Boeing AH-64 Apache helicopter. Two yokes 15 each have two blades 17 attached at opposite ends of yokes 15, and yokes 15 are pivotally attached to mast 13 for rotation therewith about mast axis 19. To provide for a pivoting connection to mast 13, two pairs of opposing cylindrical trunnions 21 extend radially from mast 13, defining flap axes 23. This configuration allows the rotor assemblies of each yoke 15 and the associated blades 17 to freely “teeter” about the corresponding flap axis 23 relative to mast 13 and to each other, as indicated by directional arrows 25.
Although there have been significant developments in rotor systems, significant room for improvement remains.
While the system of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the method to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the application as defined by the appended claims.